1. Field of the Invention
The present invention relates to a rotational angle sensor provided in a vehicle or the like for example and which is used for detecting a torque generated in a steering wheel in accordance with a steering operation of the steering wheel.
2. Description of the Related Art
A conventional rotational angle sensor, which is shown in FIG. 21, is provided with a cylindrical housing 41 made of an insulating synthetic resin and which is open at both end portions thereof. An outer wall of the housing 41 has an annular stepped portion 41a. The interior of the housing 41 is partitioned into a receptacle portion 43 and an accommodating portion 44 by means of a partition wall 42. A bearing 45 is attached to the partition wall 42 by insert molding. A rotary shaft 46 is inserted into the bearing 45 rotatably. Both end portions of the rotary shaft 46 are positioned inside the receptacle portion 43 and outside the housing 41, respectively. A rotary member 48 which supports a slider 47 is mounted on one end portion of the rotary shaft 46 positioned within the receptacle portion 43, while a lever 49 is caulked to an opposite end portion of the rotary shaft 46 at a position outside the housing 41. A ring-like seal member 50 for sealing the interior of the receptacle portion 43 is press-fitted into the accommodating portion 44.
A holder 52 with a circuit board 51 fixed thereto is press-fitted into the receptacle portion 43 from an open end of the housing 41 and is installed therein while the slider 47 is brought into sliding contact with a resistor pattern and a current collector pattern (neither shown) both formed on the circuit board 51. A terminal 53 connected to the resistor pattern and the current collector pattern (neither shown) is supported by the circuit board 51. One end portion of the terminal 53 is drawn out to the back side of the holder 52 through a hole 52a formed in the holder 52 and is soldered to a lead wire 54 which is inserted into the interior of the housing 41 through a hole 41b formed in the housing. The interior of the receptacle portion 43 is filled, on the back side of the holder 52, with an insulating adhesive 55, and the connection of the terminal 53 and the lead wire 54 is buried in the adhesive.
A method for assembling this conventional rotational angle sensor will now be described. First, the rotary member 48 with the slider 47 supported thereon is inserted into the receptacle portion 43 from an open end of the housing 41. Next, the rotary shaft 46 is inserted through the bearing 45 from the accommodating portion 44 side and the rotary member 48 is mounted to one end portion of the rotary shaft 46 by a suitable means such as press-fitting or caulking, making the rotary shaft 46 and the rotary member 48 integral with each other. Next, the sealing member 50 is press-fitted into the accommodating portion 44 of the housing 41.
Next, with one end portion of the terminal 53 drawn out to the back side of the holder 52 through the hole 52a, the circuit board 51 with the terminal 53 supported thereon is fixed to the holder 52. Then, the holder 52 is press-fitted into the receptacle portion 43 from an open end of the housing 41 and is secured to the housing. Subsequently, the lead wire 54 is inserted into the receptacle portion 43 through the hole 41b formed in the housing 41 and is soldered to one end portion of the terminal 53. Further, the insulating adhesive 55 is charged into the receptacle portion 43 and is cured, then the lever 49 is caulked to the opposite end portion of the rotary shaft 46.
Assembling of the conventional rotational angle sensor is completed in this way. After the assembly, the rotary member 48 rotates integrally with the rotary shaft 46 while the circuit board 51 is prevented its movement axially (in arrow A directions) of the rotary shaft. With rotation of the rotary member 48 the slider 47 slides on resistor and current collector patterns (not shown). Further, the insulating adhesive 55 insulates the soldered portion of the terminal 53 and the lead wire 54 from the exterior and seals the interior of the receptacle portion 43 in cooperation with the sealing member 50 to prevent the entry of dust and moisture into the receptacle portion. At the same time, the lead wire 54 is fixed to protect it sufficiently from pulling.
In the conventional rotational angle sensor thus constructed and assembled there is used, for example, a conversion mechanism (not shown) mounted on a vehicle and provided with a converter portion which converts a resistance force generated in a steering wheel (not shown) into a linear motion in proportion to a frictional force between vehicular wheels and a road surface while the steering wheel is operated. The portion located on the lever 49 side relative to the stepped portion 41a is positioned within a casing of the conversion mechanism and the lever 49 is brought into engagement with the converter portion. Further, the lead wire 54 is connected to a control circuit (not shown) which controls an electric motor (not shown) connected to the steering wheel, and with a predetermined voltage applied to resistor and current collector patterns (not shown) from the control circuit, the rotational angle sensor is used.
When a vehicle driver operates the steering wheel, a resistance force is generated in the steering wheel, and the foregoing converter portion converts this resistance force into a linear motion to rotate the rotary shaft 46 via the lever 49. With this rotation, the slider 47 slides on the resistor and current collector patterns (not shown), resulting in that a voltage corresponding to the position of the slider 47 on those patterns is outputted via the terminal 53 and the lead wire 54. In accordance with a detection signal of the resistance force thus obtained the control circuit controls the operation of the electric motor so as to diminish the resistance force. It follows that an auxiliary steering torque has been imparted to the steering wheel. Consequently, the aforesaid resistance force decreases and it is possible to lighten the burden of the vehicle driver in steering operation.
In the above conventional rotational angle sensor, however, since one end portion of the terminal 53 is spaced a distance L from the hole 41b formed in the housing 41, work is needed to conduct the lead wire 54 inserted into the receptacle portion 43 from the hole 41b further up to one end portion of the terminal 53. Thus the connecting work for connection between the terminal 53 and the lead wire 54 has so far been extremely complicated.
Further, since the connection between the lead wire 54 and the terminal 53 is required to have an extremely high tensile strength, it is necessary that the lead wire 54 be buried sufficiently into the insulating adhesive 55. Consequently, in the conventional rotational angle sensor, an axial length (in arrow A directions) of the rotary shaft 46 becomes larger. As a result, the portion located on the lead wire 54 side with respect to the stepped portion 41a projects largely from the casing of the conversion mechanism (not shown), thus giving rise to the problem that a large space for accommodating the projecting portion is required in the vehicle.
FIGS. 22 and 23 illustrate another conventional rotational angle sensor. This rotational angle sensor has a housing 101 whose interior is hollow and which comprises a cylindrical small-diameter portion 102 and a cylindrical large-diameter portion 103 both formed integrally in a stepped fashion. A bearing 104 is press-fitted in the cylindrical small-diameter portion 102 and a rotary shaft 106 with a rubber O-ring 105 fitted thereon is supported rotatably by the bearing 104. A disc-like rotary member 108 with a bifurcated slider 107 carried thereon is fitted on one end portion 106a of the rotary shaft 106, while a rotor 109 is mounted on an opposite end portion 106b of the rotary shaft with a screw 110. When the rotor 109 is rotated, the rotary member 108 rotates integrally with the rotary shaft 106.
A disc-like circuit board 111 is fitted in the housing 101 and is opposed to the rotary member 108. An arcuate resistor pattern 112 and a circular current collector pattern 113 are formed on the surface of the circuit board 111, and the slider 107 is in contact with the resistor pattern 112 and the current collector pattern 113. Terminal such as eyelet pieces (not shown) are fixed to both ends of the resistor pattern 112 and also to the current collector pattern 113, and a lead wire 115, which is connected to the terminals by solder 114, is drawn out to the exterior of the housing 101. Further, on the back side of the circuit board 111 an insulating adhesive 116 is charged into the housing 101 to seal the interior of the housing in cooperation of the O-ring 105.
A coiled spring 117 is mounted outside the cylindrical small-diameter portion 102 and is in this state placed on a top plate 103a of the cylindrical large-diameter portion 103. One end 117a of the coiled spring 117 is engaged with an engaging hole 103b formed in the top plate 103a, while an opposite end 117b thereof is engaged with the rotor 109. On the top plate 103a is provided a stopper mechanism (not shown) to restrict a rotational angle range of the rotor 109.
In the conventional rotational angle sensor thus constructed, which is mounted on a vehicle for example, there is used a conversion mechanism (not shown) provided with a converter portion which converts a resistance force generated in a steering wheel (not shown) into a linear motion in proportion to a frictional force between vehicular wheels and a road surface at the time of operating the steering wheel. The portion located on the rotor 109 side with respect to the top plate 103a is positioned within a casing of the conversion mechanism, and a tip end portion 109a of the rotor 109 is brought into engagement with the converter portion. Further, the lead wire 115 is connected to a control circuit (not shown) which controls an electric motor (not shown) connected to the steering wheel, and a predetermined voltage is applied to both ends of the resistor pattern 112 through the lead wire 115 from the control circuit. The rotational angle sensor is used in this voltage-applied state.
When the vehicle driver operates the steering wheel, a resistance force is generated in the steering wheel, but this resistance force is converted to a linear motion by the foregoing converter portion, which causes the rotor 109 to rotate against the urging force of the coiled spring 117. With this rotation, the slider 107 slides on the resistor pattern 112 and current collector pattern 113, and voltage corresponding to the position of the slider 107 on the patterns 112 and 113 is outputted through the lead wire 115. In accordance with a detection signal of the resistance force thus obtained the aforesaid control circuit controls the operation of the electric motor so as to decrease the resistance force. It follows that an auxiliary steering torque has been imparted to the steering wheel. Consequently, the resistance force decreases and it is possible to lighten the vehicle driver's burden in operating the steering wheel.
When the steering wheel has been rotated approximately four times throughout the whole of its movable range, the foregoing stopper mechanism (not shown) functions to stop rotation of the rotor 109, thereby preventing the slider 107 from protruding from an end portion of the resistor pattern 112.
When the steering wheel is operated reverse to its neutral position from its four times rotated state, the coiled spring 117, by virtue of its urging force, causes the rotor 109 to follow the motion of the foregoing converter portion, thereby preventing the occurrence of a difference (so-called hysteresis) in the aforesaid detection signal between forward and reverse rotations of the steering wheel.
In the above conventional rotational angle sensor, the coiled spring 117 is compressed during rotation of the rotor 109 and imparts an urging force to the rotor 109. In this case, with rotation of the rotor 109, the coiled spring 117 is deformed axially (in arrow A directions) of the rotary shaft 106 or radially (in arrow D directions) of the coiled spring 117 and becomes off-centered, thus causing variations in the acting direction of the urging force of the coiled spring 117 exerted on the rotor 109. Consequently, the rotor 109 cannot stably follow the motion of the foregoing converter portion, thus giving rise to a fear that the resistance force developed in the steering wheel may not be detected accurately.
Moreover, vehicular electric devices are required to be highly dust-proof, and also in the above conventional rotational angle sensor the interior of the housing 101 is sealed by both O-ring 105 and insulating adhesive 116, which seal is somewhat effective in preventing the entry of dust. However, since the O-ring 105 is deteriorated by its sliding contact with the rotary shaft 106, it is difficult to keep the interior of the housing 101 dust-proof over a long term, and thus the aforesaid seal has been unsatisfactory as a dust-proofing measure. Further, handling of the insulating adhesive 116 is troublesome and requires a long drying time. Thus, the sealing work is poor in efficiency and troublesome.